One of the most striking characteristics of primate lentiviruses and one that distinguishes them from onco- retroviruses is their ability to infect non-dividing cells including macrophages and microglia. However, the role of the macrophage reservoir in the replication and pathogenicity of primate lentiviruses such as HIV-1 are poorly understood. While most of the attention has focused on the role of the macrophage reservoir in HIV-1-mediated neuronotoxicity, the actual mechanism underscoring HIV-1-induced neuronotoxicity is not well understood. In the previous funding period, we have obtained evidence that HIV-1 commandeers cellular factors in macrophages in order to complete certain aspects of its replication cycle. In doing so, HIV- 1 alters macrophage function in a way that may have important consequences for the ability of the virus to persist within macrophages and for the ability of infected macrophages to mediate neuronotoxicity. These findings can be summarized as follows: 1. The HIV-1 accessory protein, Nef regulates the production of soluble factors by macrophages that promote viral dissemination. Nef does so by intersecting the CD40 signaling pathway. 2. CD40 activation, or Nef expression in macrophages, induces the release of neuronotoxins. 3. The HIV-1 envelope glycoprotein induces pro-inflammatory cytokine production by infected macrophages and in doing so, regulates the persistence of the infected macrophage. In the next funding period, we will extend upon these findings. Specifically, we propose to: Aim 1: Identify the viral effector domains through which the HIV-1 Nef and envelope proteins regulate macrophage function. Aim 2: Identify the cellular determinants through which Nef and envelope regulate macrophage function. Aim 3: Define how HIV-1 Nef and envelope influence viral persistence and production of neuronotoxins by infected macrophages. These studies will provide fundamental insight into the molecular mechanisms underscoring viral persistence in macrophages and induction of neuronotoxicity by infected macrophages.